Integrated circuits include analog and digital circuits made up of circuit components, such as transistors, diodes, and resistors. Sometimes, the function of one component is provided by another component, such as when transistors are configured to provide the function of a diode or a resistor.
In some logic circuits, referred to as ratioed logic circuits, resistors are connected as loads to transistors. In a ratioed logic circuit inverter, a resistive pull-up is connected to a transistor pull-down. The resistance value of the resistive pull-up is chosen to provide a low output voltage in one logic state and to charge the output to a high output voltage in the other logic state. A higher resistance value provides a lower output voltage and reduces power consumption.
In some semiconductor processes, providing a resistor with a higher resistance value consumes a large amount of valuable real estate on the integrated circuit chip. To reduce the amount of real estate used, the resistor function can be provided with a transistor, such as by connecting the drain of a metal-oxide-semiconductor field-effect-transistor (MOSFET) to its gate. In some processes, providing a higher resistance value with a drain-to-gate connected MOSFET is difficult.